Since dropping out of Stanford at age 19 to found her health-technology company Theranos in 2003, Holmes has raised $400 million and secured a deal with Walgreens.

But her success has not been without controversy. Theranos is founded on the idea that a single drop of blood can provide enough information for a complete, inexpensive blood test — a potentially world-changing development.

Yet Holmes runs her business with the secrecy typical of Silicon Valley, which may be acceptable for a social media company but is less common in the healthcare sector. Critics wondered if the hype surrounding the company and hundreds of millions of dollars pumped into it were the result of Valley hysteria rather than any real evidence. Others argued that quick blood tests in local pharmacies could foster an unhealthy culture of paranoia and hypochondria.

On Monday at the Forbes Under 30 Summit, she said that although the attacks on her credibility were difficult, she is now grateful for them, since they strengthened her resolve.

"You'll get knocked down over and over and over again, and you get back up," Holmes said. "I've been knocked down a lot, and it became really clear that this was what I wanted to do, and I would start this company over 10,000 times if I had to."

According to Forbes, Theranos has 130 more tests that have been submitted to the FDA, and its science needs to be examined in peer-reviewed journals. The criticism will not suddenly disappear.

Holmes has a long way to go to prove that Theranos is the company its investors expect it to be, but it seems that any self-doubt she may have had in her vision has evaporated and she's ready to make it a reality.